1. Field of the Invention
This invention relates to digital phase detector arrangements. Such phase detector arrangements are particularly, but not exclusively, suitable for use in digital signal interpolation, and the invention also relates to digital signal interpolator arrangements.
2. Description of the Prior Art
To change a sampled auido or video signal from one sampling frequency to another, a liner signal interpolator is required. An example of the type of conversion necessary for a video signal is the change from a sampling frequency of 13.5 MHz to 4 fsc, where fsc is the sub-carrier frequency of a PAL television signal (4.43361875 MHz). Such a conversion does not have any simple integral relationship between the two frequencies, or to put it somewhat differently, the new samples which need to be derived to form the output signal may occur almost anywhere in the time intervals between the samples of the input signal.
Such interpolation can be done using digital phase shift interpolators, but because there is no simple integral relationship between the two frequencies, an accurate means of determining the phase differences between two input clock pulse signals is essential to the process of deriving a control signal for the interpolator. Thus for digital audio and digital video applications, a phase detector is required whose output exhibits low levels of jitter; typically a jitter of less than 0.1 nsec.